Non prismatic folded roof structure

The design of a prestressed concrete roof is described. A special linear elastic analysis of non-prismatic folded structures has been applied. The obtained results have been compared to the results deducted from a small scale model test. Conclusions about the efficiency of these type of structures are shown.

Doubling the width of the platform of the San Pedro bridge in Spain

The San Pedro Bridge has six spans and is 750 m (2460 ft) long, 88 m (290 ft) high, 12 m (39 ft) wide, and curved with a radius of 700 m (2300 ft). It was built in 1993 using the cantilever method. Its super - structure is a prestressed concrete box girder with main spans of 150 m (490 ft). In 2008 and 2009, the width of the platform was enlarged to 23 m (75 ft) using five movable sets of scaffolding. The bridge remained open to traffic during construction. The original platform was widened 6 m (20 ft) on each side by connecting a new lightweight concrete cantilever to the original upper slab. These cantilevers were supported by steelstruts. The tie into the upper slab was made with new transverse post-tensioned tendons. The original superstructure was strengthened to resist the additional dead load of the expansion and live loads of the extra traffic. An additional new central web and a composite concrete-steel section were constructed and connected to the concrete box and central web using vertical high-strength post-tensioning bars. Also, external post-tensioning cables were implemented. It was also necessary to strengthen the connection of the original concrete box section to the piers. Detailed calculations were performed to evaluate the load distribution transmitted to the piers by the webs and by the original inclined concrete walls of the box girder. Finally, a detailed second-order-analysis of the complete structure was made to guarantee the resistance of the piers compared with actual loads

El pretensado : la disolución de las tipologías constructivas en la arquitectura del siglo XX

La traslación de la tecnología del pretensado desde la ingeniería civil al campo de la arquitectura da lugar a una nueva reinterpretación de las tipologías estructurales utilizadas con anterioridad, tales como los arcos, bóvedas, grandes vigas, etc. El comportamiento resistente de estos elementos estructurales se podrá desligar de su geometría, mediante la interposición de sistemas de fuerzas, escogidos por el proyectista, que se superpongan a los determinados la gravedad, de forma que el proyectista tendrá el control sobre la geometría propuesta y por tanto sobre la forma final. Estas nuevas configuraciones finales, conseguidas mediante la técnica del pretensado en el ámbito arquitectónico, tendrán a su vez un carácter formal también nuevo. Posibilitarán la construcción a grandes escalas, así como la reinterpretación de los materiales y las formas de la construcción empleadas hasta ese momento. La libertad de diseño y de escala pasa a ser entonces mucho más amplia y rica. Con el empleo de esta tecnología constructiva se puede conseguir un control estructural de tal impacto que, en relación a las tipologías estructurales tradicionales, de lugar a que la geometría de éstas no responda, con carácter necesario, a su trabajo resistente, de tal manera que se genere un nuevo conjunto de soluciones estructurales, constructivas y arquitectónicas, dando lugar con ello a la transformación o disolución de las tipologías estructurales de la tradición arquitectónica del SXX. ABSTRACT The transfer of the technology of the prestressed concrete from civil engineering to architecture has produced a new interpretation of the constructivestructural typologies traditionally used, such as bows, vaults, large beams, etc. As a result of the application of this technology the resistant behavior of such structural elements may be released from their constructive requirements as they were understood in the past. The designer will choose a system of forces, combined with the gravity, so it will be possible to control the geometry proposal and therefore the final form of the construction. These new configurations, achieved thanks to prestressing technique applied in architectural field, will also have a new formal definition, because they are detached from their structural requeriments. They will enable construction on large scales as well as the reinterpretation of materials, structures and construction forms used so far. Thereby freedom in design and scale will be broader and richer. The geometry of the structural forms, released from traditional construction types, can be controlled by this technology. So the traditional link with a priori types is broken and a new set of structural, constructive and architectural solutions appears. That is why, technology of prestressing gives the possibility of transformation, or even dissolution, of constructive typologies of the architectural tradition in the twentieth century.

Espacios máximos con recursos mínimos : edificio Central Lechera CLESA, Alejandro de la Sota

La tesis aborda el estudio de la Central lechera CLESA, uno de los edificios industriales de Alejandro de la Sota más significativos de la década de los años cincuenta en España. Las centrales lecheras fueron abordadas por Sota en distintas ocasiones entre 1955 y 1969, siendo CLESA la única de todas ellas que llega a construirse. Se trata de uno de los exponentes más brillantes de la arquitectura moderna industrial española de la posguerra, incluido en "La arquitectura de la industria, REGISTRO DOCOMOMO IBÉRICO”1 entre la veintena de edificios seleccionados de la arquitectura madrileña de este periodo. Plantea una solución singular para alcanzar la diafanidad exigida en la implantación del proceso de producción. La estructura de las naves se realiza con hormigón pretensado, siendo uno de los pioneros en la utilización de esta técnica. La hipótesis de partida considera la realidad del proyecto construido como respuesta desde la arquitectura a un programa industrial resuelto con sencillez, que partiendo de una economía de recursos que le es inherente, consigue desde la coherencia del planteamiento, soluciones donde la complejidad espacial constituye una respuesta eficaz y del máximo interés. Los objetivos de esta tesis son contribuir a un conocimiento riguroso del edificio, que permita descubrir la particularidad de su entramado espacial y el interés de las soluciones adoptadas en su configuración final, en aras de contrastar su calidad arquitectónica. El edificio de la Central Lechera CLESA, si bien es un edificio muy conocido, lo es de una manera superficial. Aparece en numerosas publicaciones, en muchas ocasiones formando parte de un relato extenso de la obra de su autor. El libro monográfico publicado en 2007 por la Fundación Alejandro de la Sota, cuya edición está a cargo de Teresa Couceiro, es la única publicación específica sobre él. Tras una breve introducción, en la que se destaca la intensa dedicación de Sota a esta obra, reúne una colección de planos, fotografías y croquis, junto a la memoria del proyecto. Ofrece una visión fragmentada, que permite vislumbrar el interés de esta obra, pero no facilita comprenderla en su integridad. Es importante destacar la publicación de CLESA en el libro editado por Pronaos (1989), que incluye una selección, realizada por el autor, de plantas, alzados y secciones que corresponden al proyecto construido junto a fotografías de la obra terminada, además de un breve texto tan conciso como esclarecedor. Sobre Alejandro de la Sota se han escrito, tesis doctorales, numerosos artículos, varios libros así como realizado exposiciones que recogen su obra global, reflejados en este documento en las consiguientes bibliografías específicas. Cabe destacar la exposición realizada en la sede del COAM en 2014, con ocasión de su centenario, que el edificio CLESA protagoniza en cierto modo, por su riesgo de desaparición.2 La tesis se estructura en cuatro capítulos: descripción, análisis, síntesis y conclusiones. El primer capítulo contempla la descripción del edificio objeto de la tesis, con una introducción que nos sitúa en el contexto histórico, económico, cultural y social en el que se desarrolla el encargo, proyecto y obra de la central lechera. La descripción propiamente dicha del conjunto industrial, partiendo del encargo de la central lechera al autor del proyecto, pasando por el anteproyecto, el proyecto visado y llegando a la obra realizada. Se compara el proyecto visado, la obra terminada y la CLESA publicada, así como el devenir del edificio. La segunda parte corresponde al análisis, en primer lugar desde el programa como planteamiento general, estudiando las circulaciones, relaciones espaciales, geométricas, esqueléticas, geográficas -parte a parte- que integran el conjunto de la central. La estructura, introducción explicativa de las soluciones adoptadas por Alejandro de la Sota; análisis del sistema esquelético del edificio por partes, operaciones geométricas y espaciales. Construcción, análisis de la materialización de la obra, sistemas constructivos empleados en cerramientos, cubiertas, lucernarios; de lo general a lo particular, estudiando los sistemas. Finalmente a través de la pequeña escala se compendian elementos singulares que forman parte de sistemas complejos, como las múltiples escaleras, barandillas, carpinterías, miradores. Se recapitula en una síntesis que configura un todo con la suma de las partes, mediante la utilización de recursos de enlace de esa arquitectura aditiva, como es el módulo, los recorridos y los enlaces visuales. El capítulo final de Conclusiones contrasta la hipótesis de partida de la tesis en cuanto a una arquitectura de espacios máximos con recursos mínimos. Recoge también diversas reflexiones como la dialéctica entre el espacio fragmentado y el espacio único; crecimiento expansivo o inclusivo; imagen singular y representación; escala doméstica y escala industrial; renuncias estructurales o limitaciones de medios. Quizás, el mayor interés de esta tesis reside los dibujos realizados en axonométrica del complejo CLESA, que han permitido restituir y reconstruir idealmente la fábrica al inicio de su actividad. Teniendo en cuenta su posible desaparición total o parcial, esta restitución cobra relevancia como testimonio de lo que fue. ABSTRACT The thesis deals with the study of CLESA's Dairy Plant, one of the most significant industrial buildings of the Decade of the fifties in Spain, by Alejandro de la Sota. The Dairies were addressed by Sota at various occasions between 1955 and 1969, being the CLESA plant the only one that is has been built. This is one of the most brilliant exponents of Spanish industrial post-war modern architecture, included in "The architecture industry, IBERIAN DOCOMOMO RECORD"3 between the score of selected buildings of Madrid architecture of this period. It poses a singular solution to achieve the openness of the space required in the implementation of the manufacturing process. The structure of the nave is done with prestressed concrete, being one of the pioneers in the use of this technique. The initial hypothesis considers the reality of the project built from the architecture in response to an industrial program solved with simplicity, that from a resource economy that is inherent, gets from the consistency of the approach, solutions where the space complexity is an effective response of great interest. The objectives of this thesis are to contribute to a rigorous knowledge of the building, which allows to discover the particularity of its space lattice and the interest of the solutions adopted in its final configuration, in order to contrast its architectural quality. The building of the Central Lechera CLESA, despite it is a well known building, is in a superficial way. It appears in several publications, often as part of an extensive account of the work of its author. The monograph published in 2007 by the Foundation Alejandro de la Sota, whose edition is run by Teresa Couceiro, is the only specific publication about it. After a brief introduction, in which Sota's intense dedication to this work stands out, it brings together a collection of drawings, photographs and sketches, along with the project report. It offers a fragmented view, which enable to glimpse the interest of this work, but not helps to understand it in full. It is important to highlight the publication of CLESA in the book edited by Pronaos (1989), which includes a selection made by the author of plants, elevations and sections corresponding to the project built, next to photographs of the finished construction, in addition to a brief text as concise as enlightening. About Alejandro de la Sota have been written doctoral thesis, numerous articles, several books as well as held exhibitions collecting his global work, which have been reflected in this document in the resulting specific bibliographies. It should be noted the exhibition in COAM headquarters in 2014, on the occasion of its Centennial, where the building CLESA has a leading role, in a certain way, because of its risk of disappearance.4 The thesis is structured in four chapters: description, analysis, synthesis, and conclusions. The first chapter provides the description of the building object of this thesis. Includes an introduction that puts us in the historic, economic, cultural and social context in which it is developed the commission, the project and construction of the dairy building. The description itself of the industrial complex, starts with the order of the dairy to the author of the project, moves through the draft, the visa project and reaches the completion of the work. The visa project, CLESA's finished and published work, as well as the future of the building is compared. The second part corresponds to the analysis, first from the program as a general approach, studying the circulations, geometric, spatial, skeletal, geographical relations - bit by bit - comprising the manufacturing plant ("la central"). The structure, explanatory introduction of the solutions adopted by Alejandro de la Sota; analysis of the skeletal system of the building by parts, geometric and spatial operations. Construction, analysis of the realization of the work, constructive systems used in the building enclosures, roofs, skylights; from the general to the particular and studying the systems. Finally through small scale unique elements that are part of complex systems, such as multiple stairs, railings, carpentry, viewpoints are summarized. It is recapitulated in a synthesis which forms a whole with the sum of the parts, using linking resources that belongs to the additive architecture, such as the module, tours and visual links The final chapter of Conclusions contrast the hypothesis of the thesis regarding the maximum space architecture with minimal resources. It also includes various reflections as the dialectic between the fragmented space and the single space; expansive or inclusive growth; unique image and representation; domestic and industrial scale; structural abandonment or limitation of means. Perhaps the greatest interest of this thesis lies in the axonometric drawings made of the CLESA complex, which ideally have allowed to restore and rebuild the factory back to the beginning of its activity. Considering its potential full or partial disappearance, such recovery becomes relevant as a testimonial evidence of what it was.

Study of the Influence of Fines on a Self-Compacting Concrete

The paper presents the results of the tests of a self-compacting concrete made with fines which include Portland cement and three fillers: hornfels, limestone and metakaolin, in a weight proportion between 23% and 45% of the admixtures. The first mix proportions were designed with a high proportion of Portland cement (720-750kg/m3), and are compared to those having a smaller content of cement and more fillers. The results obtained show that the limestone filler percentage should be higher than the hornfels one, and both of them significantly higher than that of the metakaolin so as to facilitate the fluidity and self-compactability. AIso, the higher proportion of fillers causes a rounded porosity in the mixing which has a bearing on better compressive strength results.

Evaluación de la profundidad de la fisuración superficial descendente en pavimentos asfálticos mediante técnicas de ultrasonidos. Validación teórico-práctica y modelos

La fisuración iniciada en la superficie de los pavimentos asfálticos constituye uno de los más frecuentes e importantes modos de deterioro que tienen lugar en los firmes bituminosos, como han demostrado los estudios teóricos y experimentales llevados a cabo en la última década. Sin embargo, este mecanismo de fallo no ha sido considerado por los métodos tradicionales de diseño de estos firmes. El concepto de firmes de larga duración se fundamenta en un adecuado seguimiento del proceso de avance en profundidad de estos deterioros y la intervención en el momento más apropiado para conseguir mantenerlos confinados como fisuras de profundidad parcial en la capa superficial más fácilmente accesible y reparable, de manera que pueda prolongarse la durabilidad y funcionalidad del firme y reducir los costes generalizados de su ciclo de vida. Por lo tanto, para la selección de la estrategia óptima de conservación de los firmes resulta esencial disponer de metodologías que posibiliten la identificación precisa in situ de la fisuración descendente, su seguimiento y control, y que además permitan una determinación fiable y con alto rendimiento de su profundidad y extensión. En esta Tesis Doctoral se presentan los resultados obtenidos mediante la investigación sistemática de laboratorio e in situ llevada a cabo para la obtención de datos sobre fisuración descendente en firmes asfálticos y para el estudio de procedimientos de evaluación de la profundidad de este tipo de fisuras empleando técnicas de ultrasonidos. Dichos resultados han permitido comprobar que la metodología no destructiva propuesta, de rápida ejecución, bajo coste y sencilla implementación (principalmente empleada hasta el momento en estructuras metálicas y de hormigón, debido a las dificultades que introduce la naturaleza viscoelástica de los materiales bituminosos) puede ser aplicada con suficiente fiabilidad y repetibilidad sobre firmes asfálticos. Las medidas resultan asimismo independientes del espesor total del firme. Además, permite resolver algunos de los inconvenientes frecuentes que presentan otros métodos de diagnóstico de las fisuras de pavimentos, tales como la extracción de testigos (sistema destructivo, de alto coste y prolongados tiempos de interrupción del tráfico) o algunas otras técnicas no destructivas como las basadas en medidas de deflexiones o el georradar, las cuales no resultan suficientemente precisas para la investigación de fisuras superficiales. Para ello se han realizado varias campañas de ensayos sobre probetas de laboratorio en las que se han estudiado diferentes condiciones empíricas como, por ejemplo, distintos tipos de mezclas bituminosas en caliente (AC, SMA y PA), espesores de firme y adherencias entre capas, temperaturas, texturas superficiales, materiales de relleno y agua en el interior de las grietas, posición de los sensores y un amplio rango de posibles profundidades de fisura. Los métodos empleados se basan en la realización de varias medidas de velocidad o de tiempo de transmisión del pulso ultrasónico sobre una única cara o superficie accesible del material, de manera que resulte posible obtener un coeficiente de transmisión de la señal (mediciones relativas o autocompensadas). Las mediciones se han realizado a bajas frecuencias de excitación mediante dos equipos de ultrasonidos diferentes dotados, en un caso, de transductores de contacto puntual seco (DPC) y siendo en el otro instrumento de contacto plano a través de un material especialmente seleccionado para el acoplamiento (CPC). Ello ha permitido superar algunos de los tradicionales inconvenientes que presenta el uso de los transductores convencionales y no precisar preparación previa de las superficies. La técnica de autocalibración empleada elimina los errores sistemáticos y la necesidad de una calibración local previa, demostrando el potencial de esta tecnología. Los resultados experimentales han sido comparados con modelos teóricos simplificados que simulan la propagación de las ondas ultrasónicas en estos materiales bituminosos fisurados, los cuales han sido deducidos previamente mediante un planteamiento analítico y han permitido la correcta interpretación de dichos datos empíricos. Posteriormente, estos modelos se han calibrado mediante los resultados de laboratorio, proporcionándose sus expresiones matemáticas generalizadas y gráficas para su uso rutinario en las aplicaciones prácticas. Mediante los ensayos con ultrasonidos efectuados en campañas llevadas a cabo in situ, acompañados de la extracción de testigos del firme, se han podido evaluar los modelos propuestos. El máximo error relativo promedio en la estimación de la profundidad de las fisuras al aplicar dichos modelos no ha superado el 13%, con un nivel de confianza del 95%, en el conjunto de todos los ensayos realizados. La comprobación in situ de los modelos ha permitido establecer los criterios y las necesarias recomendaciones para su utilización sobre firmes en servicio. La experiencia obtenida posibilita la integración de esta metodología entre las técnicas de auscultación para la gestión de su conservación. Abstract Surface-initiated cracking of asphalt pavements constitutes one of the most frequent and important types of distress that occur in flexible bituminous pavements, as clearly has been demonstrated in the technical and experimental studies done over the past decade. However, this failure mechanism has not been taken into consideration for traditional methods of flexible pavement design. The concept of long-lasting pavements is based on adequate monitoring of the depth and extent of these deteriorations and on intervention at the most appropriate moment so as to contain them in the surface layer in the form of easily-accessible and repairable partial-depth topdown cracks, thereby prolonging the durability and serviceability of the pavement and reducing the overall cost of its life cycle. Therefore, to select the optimal maintenance strategy for perpetual pavements, it becomes essential to have access to methodologies that enable precise on-site identification, monitoring and control of top-down propagated cracks and that also permit a reliable, high-performance determination of the extent and depth of cracking. This PhD Thesis presents the results of systematic laboratory and in situ research carried out to obtain information about top-down cracking in asphalt pavements and to study methods of depth evaluation of this type of cracking using ultrasonic techniques. These results have demonstrated that the proposed non-destructive methodology –cost-effective, fast and easy-to-implement– (mainly used to date for concrete and metal structures, due to the difficulties caused by the viscoelastic nature of bituminous materials) can be applied with sufficient reliability and repeatability to asphalt pavements. Measurements are also independent of the asphalt thickness. Furthermore, it resolves some of the common inconveniences presented by other methods used to evaluate pavement cracking, such as core extraction (a destructive and expensive procedure that requires prolonged traffic interruptions) and other non-destructive techniques, such as those based on deflection measurements or ground-penetrating radar, which are not sufficiently precise to measure surface cracks. To obtain these results, extensive tests were performed on laboratory specimens. Different empirical conditions were studied, such as various types of hot bituminous mixtures (AC, SMA and PA), differing thicknesses of asphalt and adhesions between layers, varied temperatures, surface textures, filling materials and water within the crack, different sensor positions, as well as an ample range of possible crack depths. The methods employed in the study are based on a series of measurements of ultrasonic pulse velocities or transmission times over a single accessible side or surface of the material that make it possible to obtain a signal transmission coefficient (relative or auto-calibrated readings). Measurements were taken at low frequencies by two short-pulse ultrasonic devices: one equipped with dry point contact transducers (DPC) and the other with flat contact transducers that require a specially-selected coupling material (CPC). In this way, some of the traditional inconveniences presented by the use of conventional transducers were overcome and a prior preparation of the surfaces was not required. The auto-compensating technique eliminated systematic errors and the need for previous local calibration, demonstrating the potential for this technology. The experimental results have been compared with simplified theoretical models that simulate ultrasonic wave propagation in cracked bituminous materials, which had been previously deduced using an analytical approach and have permitted the correct interpretation of the aforementioned empirical results. These models were subsequently calibrated using the laboratory results, providing generalized mathematical expressions and graphics for routine use in practical applications. Through a series of on-site ultrasound test campaigns, accompanied by asphalt core extraction, it was possible to evaluate the proposed models, with differences between predicted crack depths and those measured in situ lower than 13% (with a confidence level of 95%). Thereby, the criteria and the necessary recommendations for their implementation on in-service asphalt pavements have been established. The experience obtained through this study makes it possible to integrate this methodology into the evaluation techniques for pavement management systems.

Stress relaxation losses of prestressing steel wires

Prestressed structures are susceptible to relaxation losses which are of significant importance in structural design. After being manufactured, prestressing wires are coiled to make their storage and transportation easier. The possible deleterious effects of this operation on the stress relaxation behavior of prestressing steel wires are usually neglected, though it has been noticed by manufacturers and contractors that when relaxation tests are carried out after a long-time storage, on occasions relaxation losses are higher than those measured a short time after manufacturing. The influence of coiling on the relaxation losses is checked by means of experimental work and confirmed with a simple analytical model. The results show that some factors like initial residual stresses, excessively long-time storage or storage at high temperatures, can trigger or accentuate this damage. However, it is also shown that if the requirements of standards are fulfilled (minimum coiling diameters) these effects can be neglected.

Concrete Swelling in Two Spanish Dams

Several chemical reactions are able to produce swelling of concrete for decades after its initial curing, a problem that affects a considerable number of concrete dams around the world. Principia has had several contracts to study this problem in recent years, which have required reviewing the state-ofthe-art, adopting appropriate mathematical descriptions, programming them into user routines in Abaqus, determining model parameters on the basis of some parts of the dams’ monitored histories, ensuring reliability using some other parts, and finally predicting the future evolution of the dams and their safety margins. The paper describes some of the above experience, including the programming of sophisticated nonisotropic swelling models, that must be compatible with cracking and other nonlinearities involved in concrete behaviour. The applications concentrate on two specific cases, an arch-gravity dam and a double-curvature arch dam, both with a long history of concrete swelling and which, interestingly, entailed different degrees of success in the modelling efforts

Contribution to Theme A of the Benchmark Workshop: Effect of Concrete Swelling on the Equilibrium and Displacements of an Arch Dam

The Kariba dam is undergoing concrete expansion as a result of an alkali-aggregate reaction. The model adopted to simulate the process is explained in the paper; it is based on the model first proposed by Ulm et al, as later modified by Saouma and Perotti. It has been implemented in the commercial finite element code Abaqus and applied to solve the benchmark problem. The parameters of the model were calibrated using the data recorded up to 1995. The calibrated model was then used for predicting the evolution of the dam up to the present date. Apart from this prediction the paper offers a number of conclusions, such as the fact that the stress level appears to have a major influence on the expansion process; and it presents some suggestions to improve the formulation of the benchmark, such as providing temperature data and widening the locations and conditions of the data employed in the calibration

Polypropylene fiber-reinforced self-compacting concrete for the reconstruction of the cathedral of La Laguna, Canary Island, Spain

High performance materials are needed for the reconstruction of such a singular building as a cathedral, since in addition to special mechanical properties, high self compact ability, high durability and high surface quality, are specified. Because of the project’s specifications, the use of polypropylene fiber-reinforced, self-compacting concrete was selected by the engineering office. The low quality of local materials and the lack of experience in applying macro polypropylene fiber for structural reinforcement with these components materials required the development of a pretesting program. To optimize the mix design, performance was evaluated following technical, economical and constructability criteria. Since the addition of fibers reduces concrete self-compactability, many trials were run to determine the optimal mix proportions. The variables introduced were paste volume; the aggregate skeleton of two or three fractions plus limestone filler; fiber type and dosage. Two mix designs were selected from the preliminary results. The first one was used as reference for self-compactability and mechanical properties. The second one was an optimized mix with a reduction in cement content of 20 kg/m3and fiber dosage of 1 kg/m3. For these mix designs, extended testing was carried out to measure the compression and flexural strength, modulus of elasticity, toughness, and water permeability resistance

Effect of the curing conditions of concrete on the behaviour under freeze-thaw cycles*

The aim of this work is to relate the curing conditions of concrete and the addition of an air-entraining admixture with the damage caused by freeze–thaw cycles. In countries with a continental climate, the curing of concrete in summer is performed under climatic conditions of high temperature and low humidity, and during the winter the concrete suffers conditions of freeze–thaw, often accompanied by the use of de-icing salts. This paper shows the experimental results of the behaviour of concrete specimens cured under climatic summer conditions (high temperature and low humidity) and then subjected to freeze–thaw cycles. Curing of the specimens includes conditions of good and bad practice in relation to wetting and protection of the concrete. It also examines the effectiveness of using an air-entraining admixture in both cases. The experimental programme includes an evaluation of the mechanical properties of the concrete, the study of the cement hydration and the measurement of the volume and pore sizes of the concrete. These tests were performed before and after the application of the freeze–thaw cycles. The results obtained showed that the specimens without air-entraining admixture show a deterioration of mechanical properties after the freeze–thaw test. However, the inclusion of air bubbles benefits the behaviour of concrete against freeze–thaw cycles so even better mechanical properties after the test were observed. This anomalous behaviour is because the cement hydration process continues over the freeze–thaw tests, closing the pore structure. This aspect has been confirmed with the DTA and TG tests performed

Ductilidad del acero inoxidable bajo en níquel para estructuras de hormigón armado / Ductility in a new low nickel stainless steel for reinforced concrete

En este trabajo se presentan los diagramas tensióndeformación de un nuevo acero inoxidable con bajo contenido en níquel, un inoxidable convencional AISI 304 y un acero al carbono de uso común en estructuras de hormigón armado. Dicha ductilidad se ha estudiado determinando la tensión máxima (fmax), la tensión en el límite elástico (fy) y la deformación bajo carga máxima (εmax). Los tres materiales se han evaluado utilizando criterios aceptados internacionalmente, como son el índice p (capacidad de rotación plástica), el índice A* (área plástica de endurecimiento) y el índice de tenacidad Id (energía total absorbida en el punto de alargamiento bajo carga máxima), los resultados obtenidos se han comparado con los aceros convencionales de armaduras 500SD, 500N y 500H (EC-2).

Evaluation of the mechanical properties of self compacting concrete using current estimating models. Estimating the modulus of elasticity, tensile strength, and modulus of rupture of self compacting concrete

This study includes an analysis of the applicability of current models used for estimating the mechanical properties of conventional concrete to self-compacting concrete. The mechanical properties evaluated are: modulus of elasticity, tensile strength, and modulus of rupture. An extensive database which included the dosifications and the mechanical properties of 627 mixtures from 138 different references, was used. The models considered are: ACI, EC-2, NZS 3101:2006 (New Zealand code) and the CSA A23.3-04 (Canadian code). The precision in estimating the modulus of elasticity and tensile strength is acceptable for all models; however, all models are less precise in estimating the modulus of rupture.

Corrosion behaviour of new duplex stainless steel reinforcements embedded in chloride contaminated concrete

The use of reinforcing stainless steels (SS) in concrete have proved to be one of the most effective methods to guarantee the passivity of reinforced concrete structures exposed to chloride contaminated environment. The present research studies the corrosion behaviour of a new duplex SS reinforcements with low nickel content (LND) (more economicaly compatible) is compared with the conventional austenitic AISI 304 SS and duplex AISI 2304 SS. Corrosion behaviour of ribbed SS reinforcements was studied in mortars with chloride content (0, 0.4, 2 and 4% Cl ⎯ ) using linear polarization resistance and potentiostatic pulses technique, Ecorr and Rp values were monitored over the exposure time. The obtained icorr data for the new duplex stainless steel LND no afforded passivity breakdown after one year exposure

Impact And Explosive Loads On Concrete Buildings Using Shell And Beam Type Elements

The threat of impact or explosive loads is regrettably a scenario to be taken into account in the design of lifeline or critical civilian buildings. These are often made of concrete and not specifically designed for military threats. Numerical simulation of such cases may be undertaken with the aid of state of the art explicit dynamic codes, however several difficult challenges are inherent to such models: the material modeling for the concrete anisotropic failure, consideration of reinforcement bars and important structural details, adequate modeling of pressure waves from explosions in complex geometries, and efficient solution to models of complete buildings which can realistically assess failure modes. In this work we employ LS-Dyna for calculation, with Lagrangian finite elements and explicit time integration. Reinforced concrete may be represented in a fairly accurate fashion with recent models such as CSCM model [1] and segregated rebars constrained within the continuum mesh. However, such models cannot be realistically employed for complete models of large buildings, due to limitations of time and computer resources. The use of structural beam and shell elements for this purpose would be the obvious solution, with much lower computational cost. However, this modeling requires careful calibration in order to reproduce adequately the highly nonlinear response of structural concrete members, including bending with and without compression, cracking or plastic crushing, plastic deformation of reinforcement, erosion of vanished elements etc. The main objective of this work is to provide a strategy for modeling such scenarios based on structural elements, using available material models for structural elements [2] and techniques to include the reinforcement in a realistic way. These models are calibrated against fully three-dimensional models and shown to be accurate enough. At the same time they provide the basis for realistic simulation of impact and explosion on full-scale buildings